1. Field of the Invention
The present invention relates generally to climate control of electrical system components. More specifically, systems and methods for close coupled cooling of electrical system components such as computer systems are disclosed.
2. Description of Related Art
With the increasing density and power usage of computer systems in server farms, data centers, and collocation facilities, heat generated by the computer systems has increased and cooling systems used for heat extraction have become increasingly more complex and less direct and thus less efficient and more expensive. Heat in computer systems is generally generated by the operation of hot components such as central processing units (CPUs), memory, disk drives, power supplies, and various other high-powered, board-mounted components. As excess heat reduces the efficiency and life of the components and thus the systems, heat extraction systems are commonly employed for climate control purposes. The heat extraction systems transfer the heat generated by the hot computer components to the atmosphere or other global scale heat sink outside of the building or other enclosure housing the computers. However, the complex heat extraction systems with loosely coupled heat transfer result in increased cost and decreased cooling efficiency.
A typical heat extraction or cooling system at a collocation employs a computer room air conditioning (CRAC) system in which the air in a sealed computer room or building is cooled by one of several mechanisms that eventually transfer heat from the computer room's air to the outside environment. For example, one mechanism provides heat transfer by circulating chilled water through a cooling coil in the CRAC. Another mechanism uses a direct expansion evaporator coil in the CRAC. In both mechanisms, the computer room air is drawn into the CRAC, ducted past the chilled coils and then returned to the computer room where it can eventually remove heat from the individual components of the computers.
With a typical CRAC, cooled air may be distributed through a raised floor plenum or other distribution ducting within the computer room. For example, the CRAC may deliver cooled air through a distribution system and expel the cooled air into the computer room through a number of vented floor tiles located near the computer racks or cabinets at a substantial vertical velocity. As the air flows vertically up along the side(s) of a computer rack, fans installed in the individual computers of the computer rack cause a portion of the cooled air to flow horizontally through the individual computers which in turn cause heat transfer between the computer components and the horizontally moving cooled air. The now-heated air is exhausted from the individual computer and the computer rack and typically rises toward the ceiling of the computer room. Ideally, the heated air is directly drawn back into the CRAC by large air circulating fans. Once the air is returned to the CRAC, the air circulation path is complete and can begin again for recirculation.
Although in ideal situations such a recirculation path may achieve good efficiency, computer systems in collocations are far from ideal. For example, the normal design expectation is that over 25% of the cooled air never reaches the computer components that the cooled air is intended to cool. In actual installed systems, as much as 50% of the cooled air may fail to reach the hot computer components.
Several factors contribute to the inefficiency. For example, chilled air can short circuit, i.e., flow directly from the vented floor tiles to the ceiling, and be drawn back into the CRAC before it passes through the computer racks to cool the individual components. As another example, the computer room may contain many leaks, such as those resulting from electrical and other utility connections that require penetrations through the walls of the computer room, that allow the cooled air to escape into spaces that are not intended to be conditioned. As yet another example, the air exiting the CRAC is often at temperatures as low as 50° F. while temperatures on the outside of the computer room's walls, ceiling, and floor can be at temperatures above 80° F. As a result of the high temperature gradients as well as the typical lack of insulation and large surface areas of the walls, ceiling, and floor, the exterior heat transferred into computer room is also transferred to the cooled air before and/or after the cooled air has circulated past the components of the individual computers. Various other factors also contribute to the inefficiency of typical CRAC systems. The inefficiencies greatly add to the cost as the heat transfer systems must have correspondingly larger cooling capacities which in turn require corresponding larger power usages.
Thus what is needed is a cost effective and reliable cooling or heat transfer system such as for cooling computer systems. Ideally, the cooling or heat transfer system also allows for quick, easy, and inexpensive repair and replacement of computer components and computer systems.